1. Incorrect GSTIN of Supplier or Recipient

The Problem

Every GST-registered business has a 15-digit GSTIN number. While creating an invoice, many people type the wrong GSTIN. Sometimes they mix up numbers like “0” and letter “O”. Sometimes they enter a GSTIN that is cancelled or inactive.

If the GSTIN is incorrect:

• The buyer may not get Input Tax Credit.
• The invoice will not match GST records.
• You will get a notice from GST department.

The Simple Solution

Before creating GST invoice, always check the GSTIN on official GST website using the “Search Taxpayer” option.

If you use billing software, turn on GSTIN auto-check or auto-fill features. This reduces typing mistakes.

Taking one minute to verify GSTIN can save you from future trouble.

2. Mistakes in HSN Code or Tax Rates

The Problem

Every product and service has an HSN code and a fixed GST rate like 5%, 12%, 18%, or 28%. Many businesses use the wrong HSN code or apply the wrong tax rate.

For example:

• Charging 18% instead of 5%
• Using an old tax rate
• Selecting the wrong product category

This usually happens when businesses do not update their tax data regularly.

The Simple Solution

Keep an updated list of HSN codes and GST rates in your billing software.

Check GST rate changes regularly from official CBIC notifications. If you are not sure about the tax rate, confirm before issuing the invoice.

Using updated data helps you avoid overcharging or undercharging tax.

3. Incorrect Invoice Numbering (Duplicate or Non-Sequential)

The Problem

GST rules say that invoice numbers must be:

• Unique
• In proper sequence
• Not repeated
• Maximum 16 characters

Some businesses accidentally:

• Use the same invoice number twice
• Skip numbers in between
• Add special symbols not allowed under GST

This can create confusion during audits and GST return filing.

The Simple Solution

Use accounting software that automatically generates invoice numbers in order.

Do not manually edit invoice numbers unless necessary.

Make sure:

• Numbers follow a proper sequence
• They are not longer than 16 characters
• Only “-” or “/” symbols are used if needed

Automatic numbering makes compliance easy.

4. Wrong Place of Supply (IGST vs. CGST/SGST)

The Problem

GST has different tax types:

• CGST and SGST for sales within same state
• IGST for sales between different states

Many businesses apply the wrong tax type.

For example:

• Charging CGST and SGST for inter-state sales
• Charging IGST for intra-state sales

This usually happens when the place of supply is not checked properly.

The Simple Solution

Look at the first two digits of the customer’s GSTIN. These digits show the state code.

If the seller and buyer are in the same state → Charge CGST + SGST.
If they are in different states → Charge IGST.

In special cases like “Bill-to Ship-to” transactions, check carefully before selecting the tax type.

Correct tax selection prevents return mismatches.

5. Missing or Incorrect e-Invoice Details (IRN/QR Code)

The Problem

Business with the turnover above ₹5 crore will must generate the e-invoices for the B2B transactions.

Some businesses:

• Forget to generate Invoice Reference Number (IRN)
• Do not include QR code
• Enter incorrect details like wrong PIN code
• Create normal invoice instead of e-invoice

If IRN is not generated, the invoice is considered invalid under GST rules.

The Simple Solution

If your business crosses the required turnover limit:

• Generate invoices through the official e-invoice system
• Use API-based integration with the e-invoice portal
• Ensure IRN and QR code are generated properly

Using automated integration reduces mistakes and saves time.

Why Avoiding These Invoice Mistakes Is Important?

Mistakes in GST invoices can cause:

• Rejection of Input Tax Credit
• GST notices
• Penalties and interest
• Return mismatches
• Extra work during audit

Even small typing errors can create big problems later.

By checking details carefully and using proper accounting software, you can avoid most of these issues.